The present invention relates to polishing and planarization of semi-conductor wafers. More particularly, the present invention relates to a method and apparatus for linearly reciprocating at least a portion of a continuous polishing member to polish a semiconductor wafer.
Semiconductor wafers are typically fabricated with multiple copies of a desired integrated circuit design that will later be separated and made into individual chips. A common technique for forming the circuitry on a semiconductor is photolithography. Part of the photolithography process requires that a special camera focus on the wafer to project an image of the circuit on the wafer. The ability of the camera to focus on the surface of the wafer is often adversely affected by inconsistencies or unevenness in the wafer surface. This sensitivity is accentuated with the current drive toward smaller, more highly integrated circuit designs. Semiconductor wafers are also commonly constructed in layers, where a portion of a circuit is created on a first level and conductive vias are made to connect up to the next level of the circuit. After each layer of the circuit is etched on the wafer, an oxide layer is put down allowing the vias to pass through but covering the rest of the previous circuit level. Each layer of the circuit can create or add unevenness to the wafer. This unevenness is preferably smoothed out before generating the next circuit layer.
Chemical mechanical planarization (CMP) techniques are used to planarize the raw wafer and each layer of material added thereafter. Available CMP systems, commonly called wafer polishers, often use a rotating wafer holder that brings the wafer into contact with a non-abrasive polishing pad moving in the plane of the wafer surface to be planarized. A polishing fluid, such as a chemical polishing agent or slurry containing microabrasives, is applied to the polishing pad to polish the wafer. The wafer holder then presses the wafer against the rotating polishing pad and is rotated to polish and planarize the wafer. Another type of polisher is a linear polishing mechanism that rotates a polishing pad mounted on an endless loop. This type of polisher also utilizes an abrasive slurry to chemically-mechanically planarize or polish semiconductor wafers. With the recent introduction of fixed abrasive polishing media that does not require an abrasive slurry in order to planarize or polish a semiconductor wafer, new wafer polishers are desirable that can take advantage of the fixed abrasive media.